In human nutrition—as far as regions where heart disease is a more common cause of death[?] than starvation are concerned—animal fats are generally considered unhealthy due to their association with high cholesterol levels in the blood. Animal fat contains some cholesterol, but saturated fat (a large component of animal fat) stimulates cholesterol production in humans and so animal fat contributes in two ways to cholestrol levels. While elevated blood cholesterol levels have been linked to heart disease, it should be noted that there is no necessary relationship between cholesterol intake and blood cholesterol level. (A properly functioning liver regulates the blood cholesterol level by storing and releasing as well as producing and excreting cholesterol as appropriate (primarily as bile). Even vegans, whose dietary intake of cholesterol is by definition essentially zero, have cholesterol in their blood.)